Method and apparatus for wavefront sensing
A method for performing optical wavefront sensing includes providing an amplitude transmission mask having a light input side, a light output side, and an optical transmission axis passing from the light input side to the light output side. The amplitude transmission mask is characterized by a checkerboard pattern having a square unit cell of size Λ. The method also includes directing an incident light field having a wavelength λ to be incident on the light input side and propagating the incident light field through the amplitude transmission mask. The method further includes producing a plurality of diffracted light fields on the light output side and detecting, at a detector disposed a distance L from the amplitude transmission mask, an interferogram associated with the plurality of diffracted light fields. The relation 0 < L < 1 8 Λ 2 λ or 1 4 Λ 2 λ ( 2 n - 1 ) < L < 1 4 Λ 2 λ ( 2 n + 1 ) is satisfied, where n is an integer greater than zero.
1. A wavefront sensor comprising:
an amplitude-only transmission mask characterized by a checkerboard pattern having a unit square cell of size Λ;
a detector disposed at a distance, L, from the amplitude-only transmission mask and optically downstream of the amplitude-only transmission mask,
wherein
0
<
L
<
1
8
Λ
2
λ
or
1
4
Λ
2
λ
(
2
n
-
1
)
<
L
<
1
4
Λ
2
λ
(
2
n
+
1
)
,
where λ is a wavelength of an incident field and n is a positive integer; and
a computer coupled to the detector.
2. The wavefront sensor of claim 1 wherein the computer includes a non-transitory computer-readable storage medium comprising a plurality of computer-readable instructions tangibly embodied on the computer-readable storage medium, which, when executed by a data processor, provide a measurement of characteristics of a wavefront of an incident beam, the plurality of instructions comprising:
instructions that cause the data processor to obtain an interferogram associated with the incident beam passing through a transmission mask;
instructions that cause the data processor to Fourier transform the interferogram to provide a frequency domain interferogram;
instructions that cause the data processor to select a subset of harmonics from the frequency domain interferogram;
instructions that cause the data processor to individually inverse Fourier transform each of the subset of harmonics to provide a set of spatial domain harmonics;
instructions that cause the data processor to extract a phase profile from each of the set of spatial domain harmonics;
instructions that cause the data processor to remove phase discontinuities in the phase profile;
instructions that cause the data processor to rotate the phase profile; and instructions that cause the data processor to reconstruct a phase front of the wavefront of the incident beam.
3. The wavefront sensor of claim 1 , wherein the detector is characterized by a pixel size and Λ is about 10 times larger than the pixel size.
4. The wavefront sensor of claim 1 , wherein 10 nm<λ<2,000 nm.
5. The wavefront sensor of claim 1 , wherein 1 mm≤L≤10 mm.
6. The wavefront sensor of claim 1 , wherein the amplitude-only transmission mask comprises a chrome layer.
7. The wavefront sensor of claim 6 , wherein the amplitude-only transmission mask further comprises a silica substrate.
8. The wavefront sensor of claim 1 , further comprising a 12-bit camera, wherein the amplitude-only transmission mask is directly attached to the 12-bit camera.
9. The wavefront sensor of claim 1 , wherein the computer includes a non-transitory computer-readable storage medium comprising a plurality of computer-readable instructions tangibly embodied on the computer-readable storage medium, which, when executed by a data processor, provide a measurement of characteristics of a wavefront of an incident beam, the plurality of instructions comprising instructions that cause the data processor to obtain an interferogram associated with the incident beam passing through a transmission mask.
10. The wavefront sensor of claim 9 , wherein the computer-readable instructions, when executed by the data processor, further provide instructions comprising instructions that cause the data processor to Fourier transform the interferogram to provide a frequency domain interferogram.